Supplementary material to "Chemical composition and light absorption of carbonaceous aerosols emitted from crop residue burning: Influence of combustion efficiency"

Abstract. The East China experiences extensive crop residue burning in fields during harvest seasons. The direct radiative effect (DRE) of carbonaceous aerosols from crop residue burning in June 2013 in East China was investigated using the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem). Absorption of organic aerosol (OA) in the presence of brown carbon (BrC) was considered using the parameterization of Saleh et al. (2014), in which the imaginary part of BrC refractive index was a function of the ratio of the black carbon (BC) and OA and wavelengths. The carbonaceous emissions from crop fires were estimated using the Moderate Resolution Imaging Spectroradiometer (MODIS) fire radiative power products with a localized crop burning-sourced BC-to-organic carbon (OC) ratio emission ratio of 0.27. The simulation results were evaluated with in situ measurements of fine particle (PM2.5) chemical components and meteorological observations. The aerosol optical depths were comparable with MODIS detections. The BC and OC peak concentrations reached 34.3 µg m−3 and 121.1 µg m−3, of which the crop residue burning contributed 86 % and 90 %, respectively. Correspondingly, the DREs of crop residue burning-sourced BC and BrC (due to absorption) reached +20.16 W m−2 and +7.17 W m−2, respectively. On average, during the harvest season, crop residue burning introduced a DRE of +0.39 W m−2 throughout East China. We found that BrC absorption and BC introduced significant positive DREs, +0.85 W m−2 and +1.05 W m−2, respectively. The BrC DRE due to scattering was stronger (−1.1 W m−2) than its DRE due to absorption. The sensitivity test showed that the BrC DRE strongly depended on the absorptivity and BC-to-OA ratio emission ratio from crop residue burning, and the volume mixing treatment could result in a higher positive DRE compared to the core/shell treatment.

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Chemical composition and light absorption of carbonaceous aerosols emitted from crop residue burning: influence of combustion efficiency

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-13721-2020 ◽

2020 ◽

Vol 20 (22) ◽

pp. 13721-13734

Author(s):

Yujue Wang ◽

Min Hu ◽

Nan Xu ◽

Yanhong Qin ◽

Zhijun Wu ◽

...

Keyword(s):

Organic Carbon ◽

Biomass Burning ◽

Light Absorption ◽

Combustion Efficiency ◽

Emission Factors ◽

Absorption Efficiency ◽

Water Soluble ◽

Radiation Budget ◽

Carbonaceous Aerosols ◽

Flaming Combustion

Abstract. Biomass burning is one of the major sources of carbonaceous aerosols, which affects air quality, the radiation budget and human health. Field straw residue burning is a widespread type of biomass burning in Asia, while its emissions are poorly understood compared with wood burning emissions. In this study, lab-controlled straw (wheat and corn) burning experiments were designed to investigate the emission factors and light absorption properties of different biomass burning organic aerosol (BBOA) fractions, including water-soluble organic carbon (WSOC), humic-like substances (HULIS) and water-insoluble organic carbon (WISOC). The influences of biofuel moisture content and combustion efficiency on emissions are comprehensively discussed. The emission factors of PM2.5, organic carbon (OC) and elemental carbon (EC) were 9.3±3.4, 4.6±1.9 and 0.21±0.07 g kg−1 for corn burning and 8.7±5.0, 3.9±2.8 and 0.22±0.05 g kg−1 for wheat burning, generally lower than wood or forest burning emissions. Though the mass contribution of WISOC to OC (32 %–43 %) was lower than WSOC, the light absorption contribution of WISOC (57 %–84 % at 300–400 nm) surpassed WSOC due to the higher mass absorption efficiency (MAE) of WISOC. The results suggested that BBOA light absorption would be largely underestimated if only the water-soluble fractions were considered. However, the light absorption of WSOC in the near-UV range, occupying 39 %–43 % of the total extracted OC absorption at 300 nm, cannot be negligible due to the sharper increase of absorption towards shorter wavelengths compared with WISOC. HULIS were the major light absorption contributors to WSOC, due to the higher MAE of HULIS than other high-polarity WSOC components. The emission levels and light absorption of BBOA were largely influenced by the burning conditions, indicated by modified combustion efficiency (MCE) calculated by measured CO and CO2 in this study. The emission factors of PM2.5, OC, WSOC, HULIS and organic acids were enhanced under lower MCE conditions or during higher moisture straw burning experiments. Light absorption coefficients of BBOA at 365 nm were also higher under lower MCE conditions, which was mainly due to the elevated mass emission factors. Our results suggested that the influence of varied combustion efficiency on particle emissions could surpass the differences caused by different types of biofuels. Thus, the burning efficiency or conditions should be taken into consideration when estimating the influence of biomass burning. In addition, we observed that the ratios of K+/OC and Cl-/OC increased under higher MCE conditions due to the enhancement of potassium and chlorine released under higher fire temperatures during flaming combustion. This indicates that the potassium ion, as a commonly used biomass burning tracer, may lead to estimation uncertainty if the burning conditions are not considered.

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Estimation of lifetime of carbonaceous aerosol from open crop residue burning during Mount Tai Experiment 2006 (MTX2006)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-14363-2012 ◽

2012 ◽

Vol 12 (6) ◽

pp. 14363-14392 ◽

Cited By ~ 5

Author(s):

X. L. Pan ◽

Y. Kanaya ◽

Z. F. Wang ◽

Y. Komazaki ◽

F. Taketani ◽

...

Keyword(s):

Organic Carbon ◽

Black Carbon ◽

Crop Residue ◽

Water Soluble ◽

Carbonaceous Aerosol ◽

East China ◽

Biomass Combustion ◽

Carbonaceous Aerosols ◽

Geographical Regions ◽

Crop Residue Burning

Abstract. Studying the emission ratios of carbonaceous aerosols (element carbon, EC, and organic carbon, OC) from open biomass burning helps to reduce uncertainties in emission inventories and provides necessary constraints for model simulations. We measured apparent elemental carbon (ECa) and OC concentrations at the summit of Mount Tai (Mt. Tai) during intensive open crop residue burning (OCRB) episodes using a Sunset OCEC analyzer. Equivalent black carbon (BCe) concentrations were determined using a Multiple Angle Absorption Photometer (MAAP). In the fine particle mode, OC and EC showed strong correlations (r > 0.9) with carbon monoxide (CO). Footprint analysis using the FLEXPART_WRF model indicated that OCRB in central east China (CEC) had a significant influence on ambient carbonaceous aerosol loadings at the summit of Mt. Tai. ΔECa/ΔCO ratios resulting from OCRB plumes were 14.3 ± 1.0 ng m−3 ppbv−1 at Mt. Tai. This ratio was more than three times those resulting from urban pollution in CEC, demonstrating that significant concentrations of soot particles were released from OCRB. ΔOC/ΔCO ratio from fresh OCRB plumes was found to be 41.9 ± 2.6 ng m−3 ppbv−1 in PM1. The transport time of smoke particles was estimated using the FLEXPART_WRF tracer model by releasing inert particles from the ground layer inside geographical regions where large numbers of hotspots were detected by a MODIS satellite sensor. Fitting regressions using the e-folding exponential function indicated that the removal efficiency of OC (normalized to CO) was much larger than that of ECa mass, with mean lifetimes of 27 h (1.1 days) for OC and 105 h (4.3 days) for ECa, respectively. The lifetime of black carbon estimated for the OCRB events in east China was comparably lower than the values normally adopted in the transport models. Short lifetime of organic carbon highlighted the vulnerability of OC to cloud scavenging in the presence of water-soluble organic species from biomass combustion.

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